I'm experiencing the same with the 3 captured Gaul settlements to the North, Genua, Mediolanum and Patavium, they're all now well developed and allow plenty of opportunity to reinforce the 4 legions stationed close by who's job it is to hold back the Gaul tide from the West. I gave up counting the dead long ago, they just keep coming ....
Also because i'm staying put and on the defensive, the coffers are filling up nicely. Slaying Gaul armies and retraining the battle-hardened legions isn't too much of a costly business actually.
On a sidenote: Money i've saved has been spent on 2 fleets and a legion complete with reserves and dispatched to Briton, or what is now modern day Ireland.
The garrison was wipped out using partial reserves and merc units i hired on arrival. Once i have the population under control, which is proving difficult due to the disadvantages of Distance to Capital and Culture Penalties etc, i plan to use the town as a forward base for conquering the rest of Briton .... unhindered by Carthage, Gaul, Greeks or anyone else i'm currently at war with!